This invention relates to a cylinder for a rotary web processing machine, and in particular to a cylinder which is constituted by a mandrel and a plurality of cutting and/or creasing rings detachably fixed thereto.
Rotary web processing machines are used for creasing and/or cutting webs of board, for example, for forming carton blanks. Such a machine has a pair of cylinders which are rotatably mounted in a frame in such a manner that the rings of the two cylinders are in alignment. The web to be processed is passed through the nip between the two cylinders, so that the web is creased and/or cut as it passes through the machine.
When cutting and/or creasing webs to form carton blanks, it is common practice to separate the functions of longitudinal cutting and/or creasing from those of transverse cutting and/or creasing. This is in order to alter one set of functions without affecting the other, or to facilitate independent adjustment of the penetration of the creasing and/or cutting surfaces of the rings into the web. In particular, it is often important to be able to move each of the rings accurately and interchangeably into different predetermined positions. Moreover, many rotary web processing machines require frequent ring changes to be made. For example, when making milk carton blanks, it is frequently desirable to change the lateral pitch of the creasing rings which form the tops and bases of the cartons. By changing the lateral positions of these creasing rings, it is possible to make milk cartons which have the same repeat lengths but are of different predetermined widths.
The cylinders of many known rotary web processing machines have one-piece creasing rings which are threaded onto a key-wayed mandrel, the lateral positions of the rings being determined by spacing rings (or tubes) positioned between adjacent pairs of creasing rings. Consequently, when it is required to re-position the creasing rings on the mandrel of such a cylinder, it is necessary to carry out the following steps:
(a) the mandrels must be removed from the web processing machine; PA1 (b) the creasing rings and spacing rings must then be removed from the mandrels; PA1 (c) the creasing rings must be replaced on the mandrels with different spacing rings positioned therebetween; and PA1 (d) the mandrel must then be repositioned in the web processing machine.
Obviously, this process is very time consuming, and so is extremely disadvantageous when frequent ring changes must be made.
In order to avoid the difficulties with this type of cylinder, it is known to use two-part creasing rings which can be clamped to a mandrel in a variety of positions. The two parts (segments) of each ring can be drawn together to clamp that ring to the mandrel using parallel screws across the adjoining surfaces of the segments. This method of drawing the segments together is often inconvenient, in that it is difficult to arrange for the screw heads to be accessibly positioned on the periphery of the segments. Moreover, although the rings can generally be positioned anywhere along the axis of the mandrel, radial location is difficult. Thus, radial location is generally provided by a key and slot arrangement between the mandrel and each ring, and this is invariable without the provision of further attachments. The rings may be held in predetermined positions by means of spacers positioned therebetween. Alternatively, this can be accomplished by dowel pins fixed to the segments and extending towards the corresponding segments of the adjacent ring.
Alternatively, the segments of each ring can be fixed to the mandrel by radial screws. In this case, two dowel pins are used for axial and radial location of each of the segments. Here again, however, it is extremely difficult to vary the radial location of each of the rings. In particular, unless the two dowel pins of each segment are parallel, they would have to be retractable to enable the segments to be removed. Retractable dowel pins complicate the arrangement and add to the number of steps required to fit and remove the rings. Thus, when frequent ring changes are necessary, this type of fitting is disadvantageous. Moreover, the constant insertion and removal of the dowel pins leads to excessive wear of the bores provided for them in the mandrel. The provision of parallel dowel pins would mean providing non-radial bores in the mandrel, and this would entail great difficulties in ensuring accurate radial location of the rings in interchangeable positions. Thus, although cylinders of this type permit relatively easy axial repositioning of the creasing rings, they suffer from a major disadvantage that it is extremely difficult, if not impossible, to position the creasing rings accurately (in both radial and axial directions) in different predetermined positions. Moreover, cylinders of this type are not suitable where frequent ring changes are necessary. (Cylinders of this type are described in U.S. Specification No. 1547214 & GB Patent Specification No. 871450).
The aim of the invention is to provide a cylinder for a rotary web processing machine whose rings can easily be removed and re-positioned accurately in both radial and axial directions, without requiring its mandrel to be removed from its bearings.